Device for the continuous manufacture of slabstock polyurethane foam

ABSTRACT

The present invention relates to a device for the continuous manufacture of slabstock polyurethane foam including a conveyor means (1), a mixing head (51) and means (6) for discharging the reaction mixture from the mixing head (51) onto the conveyor means (1). The device further includes a start board (7), a stop board, means for moving the start board (7) along the conveyor means at the beginning of a production run in such a manner that it obstructs the moving reaction mixture to thereby increase the height of the first portion of the produced foam, and means for moving the stop board at the end of a production run in such a manner that it pushes the foaming reaction mixture ahead to thereby increase the height of the end portion. In this way, no operator has to enter the foaming machine and the start and end profiles of the foam blocks are optimised.

The present invention relates to a device for the continuous manufactureof slabstock polyurethane foam comprising conveyor means, a mixing headfor mixing polyurethane reaction components containing a blowing agent,means for discharging said reaction mixture onto said conveyor means andmeans for driving said conveyor means.

Such a device is generally known. In practice, use is made of differenttypes of continuous foaming machines including the conventional inclinedconveyor machines, either with or without planiblock, maxfoam andvarimax machines. A problem with these known continuous foam productionmachines is that a manual operation is required as well at the beginningof a foam production run as at the end thereof in order to obtain auseful front and end portion of the slabstock foam. Without the manualintervention of an operator, both the first and the last foam portion ofa production run would decline slowly to the respective extremity of theslabstock foam resulting in a loss of several meters of foam.

In the known machines, the operators use for example a board fixed atthe end of a long pole to retain the first portion of reaction mixturewhile they stand on the first conveyor. As the conveyor starts running,the start board retaining the foaming reaction mixture moves also overthe conveyor means. At the end of a production run, the operators pushthe last portion of reaction mixture forwards in order to obtain an endportion of the desired height.

A drawback of the known devices consists in that in some cases theoperators have to enter the foaming machines both at the start and atthe end of a production run to realize the desired foam profile. It isclear that this may be dangerous and harmful to their health due to theproduction of noxious gases during the foam process.

Moreover, the obtained foam profile depends on the skill and experienceof the operator. In fact, the operator has no direct control of the foamheight but the effect of the manual manipulation of the foaming reactionmixture can only be seen after a certain time, more particular after thetime required by the foam to reach its final height. Further, the riseprocess of the reaction mixture depends on its composition, and moreparticularly on its blowing agent content, so that this composition hasalso to be taken into account when manipulating the reaction mixture toobtain the desired foam profile.

An object of the present invention is to provide a device for thecontinuous manufacture of slabstock polyurethane foam which allowscontrol of the foam profile at the beginning and the end of a productionrun without requiring operators to enter the foaming machine and whichoptimises the start and end profile of the foam blocks.

To this end, a device according to the invention is characterised inthat it comprises moreover a start board and a stop board, means forpositioning said start board transversely onto said conveyor means nearthe place of discharge of said reaction mixture at the beginning of aproduction run, means for moving the start board along said conveyormeans in such a manner that the start board obstructs, in a first phase,the reaction mixture moving over said conveyor means to thereby increasethe height of the front portion of the produced slabstock polyurethanefoam more particularly so that this front portion will substantiallyhave the same height as a subsequent portion after full rise expansion,and in such a manner that it moves, in a second phase, substantially atthe same speed as said conveyor means, means for removing the startboard from said conveyor means after the front portion of the producedfoam retains sufficiently its shape, means for positioning the stopboard transversely onto said conveyor means near the place of dischargeof said reaction mixture after the reaction mixture discharge isstopped, means for moving the stop board along said conveyor means afterthe positioning of said stop board so as to push the foaming reactionmixture ahead relative to said conveyor means to thereby increase theheight of the end portion of the produced slabstock polyurethane foam,more particularly in such a manner that this end portion will havesubstantially the same height as a previous portion after full riseexpansion.

The hereabove defined means of the device according to the inventionenable a mechanical control of the start and end profile of the producedfoam block so that these profiles do not depend any more on the manualmanipulation of the operators. An important advantage of such amechanical control is further that it allows control of the start andend profiles in a completely enclosed foam production machine, forexample in a machine described in PCT-Patent Application n°PCT/EP91/02176 of the same applicant.

In a preferred embodiment of the device according to the invention saidstart board moving means are provided for maintaining the start board,in said first phase, in a standstill position and for starting to movethe start board, substantially at the same speed as said conveyor means,as the foaming reaction mixture reaches a predetermined height againstthe start board.

In a particular embodiment of the device according to the invention,said stop board positioning means are adapted to position said stopboard within a distance of 3 m, and preferably within a distance of 0.5m, from the place of discharge of the reaction mixture.

In a further particular embodiment of the device according to theinvention, said start board positioning means are adapted to positionsaid start board within a distance of 3 m, preferably within a distanceof 1.5 and in particular within a distance of 0.5 m from the place ofdischarge.

Other details and advantages of the invention will become apparent fromthe following description of some embodiments of a device for thecontinuous manufacture of slabstock polyurethane foam according to theinvention. This description is only given by way of illustrative exampleand is not intended to limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The reference numerals used in this description relate to the annexeddrawings wherein:

FIG. 1 shows schematically a longitudinal sectional view of a deviceaccording to the invention, including the start board and the startboard control means;

FIG. 2 is a schematical top plan view of the device as shown in FIG. 1;

FIGS. 3 and 4 are side elevational views of a variant embodiment of thestart board of FIG. 1 in two different positions;

FIG. 5 is a longitudinal sectional view corresponding to FIG. 1 butshowing the stop board and the stop board control means instead of thestart board and start board control means;

FIG. 6 is a schematical top plan view of the device as shown in FIG. 5;and

FIGS. 7 and 8 show schematically a longitudinal sectional view of adevice analogous to the device shown in FIGS. 1 and 5 but wherein thestart board and stop board are one and the same board.

FIGS. 9 and 10 are longitudinal sectional views of the anchoringmechanism of a bottom sheet on the first bottom conveyor showing thismechanism in two different positions.

In these figures, the same reference numerals are used for the same oranalogous elements.

The device for the continuous manufacture of slabstock polyurethane foamaccording to the present invention comprises, in general, conveyormeans, a mixing head for mixing polyurethane reaction componentscontaining a blowing agent, means for discharging said reaction mixtureonto said conveyor means and means for driving said conveyor means. Thisdevice can be of different types including the inclined conveyor type(with and without planiblock), the Maxfoam type and the Varimax type. Itis therefore clear that the invention is not limited to any one of thesetypes, although the drawings represent only a Maxfoam machine.

The conveyor means 1 of the Maxfoam machine shown in the figures,comprise a fall-plate 2, a first bottom conveyor 3 and a bottom sheet 4disposed longitudinally over the fall-plate 2 and the first bottomconveyor 3. The mixing head, indicated by reference 51, is connected bymeans of a duct 5 to the bottom of a trough 6. The reaction mixturesupplied to this trough 6 foams up and arrives onto the bottom sheet 4,at the beginning of the fall-plate 2. During its transport over themoving conveyor means 1, the reaction mixture rises further andpolymerizes to produce a foam block.

In order to obtain the desired block profile at the beginning and theend of a production run, i.e. a foam block, the height of which issubstantially uniform towards the extremities of the block, the deviceaccording to the invention comprises a start board 7 and a stop board 8and means for mechanically controlling the movements of these boards 7and 8.

These control means comprise means for lowering and positioning thestart board 7 at the beginning of a production run transversely onto theconveyor means 1 near the place of discharge of the reaction mixture,i.e. near the trough 6. The start board positioning means do not have tobe fully mechanical but may need a manual manipulation of the operatorssince at the beginning of a production run, there is not any productionof noxious gases yet so that the operators can enter the foaming machinewithout any risk.

The control means further comprise means for moving the start board 7along the conveyor means 1 in such a manner that the start board 7obstructs, in a first phase, the reaction mixture moving over theconveyor means 1 and that its speed is, in a second phase, substantiallyequal to the speed of the conveyor means 1. During said first phase, thereaction mixture is accumulated by the start board in order to increasethe height of the front portion of the produced slabstock polyurethanefoam, in particular so that this front portion has substantially thesame height as a subsequent portion after full rise expansion.

The start board 7 may obstruct the foaming reaction mixture by moving ata smaller speed than the conveyor means 1. In a preferred embodiment,however, the start board 7 is maintained in a standstill position duringsaid first phase. The second phase, wherein the start board 7 is movingat the same speed as the conveyor means 1, is then started as thefoaming reaction mixture reaches a predetermined height against thestart board 7. This moment can be determined, so that the start of aproduction run can be repeated each time in the same way. Moreover, saidpredetermined height can also be adjusted on the basis of the foamingproperties of the reaction mixture. Preferably, the movement of theconveyor means 1 is started synchroneously with the movement of thestart board 7.

In an effective embodiment, the start board positioning means areadapted to position the start board 7 within a distance of 3 m from theplace of discharge of the reaction mixture, i.e. of the edge of thetrough 6. Preferably, the start board 7 is positioned within a distanceof 1.5 and in particular within a distance of 0.5 from the place ofdischarge. In this way the reaction mixture can be accumulatedsufficiently by means of the start board 7 to obtain the desired height.

The device according to the invention comprises further means forremoving the start board 7 from the conveyor means 1 after the producedfoam retains sufficiently its shape or has in other words a sufficientdimensional stability.

The start board removing means comprise in particular means foraccelerating the start board 7 in the travel direction of the foam andmeans for lifting the start board 7 after a sufficient gap is createdbetween the front of the foam and the start board.

At the end of a production run, the stop board 8 is positionedtransversely over the conveyor means, near the place of discharge of thereaction mixture by means of stop board positioning means. These meansare adapted in particular to position the stop board within a distanceof 0.5 m from the place of discharge of the reaction mixture. In thisway, the final portion of the reaction mixture can be pushed forwardsover the conveyor means in order to increase the height of the end ortail portion of the produced foam block. To this end, the devicecomprises means for moving the stop board 8 along the conveyor means ata speed higher than the speed of the conveyor means 1. In a conventionalinclined foam machine, the conveyor means can be stopped at the momentthe reaction mixture discharge is stopped. In a Maxfoam machine, themovement of the conveyor means is preferably stopped as the last portionof the reaction mixture is transported upto the first conveyor belt 3.

In the device shown in FIGS. 1 and 2 the start board 7 is connected bymeans of a first link arm 9 to a carriage 10 which is movable over afirst overhead track 11 by means of a first variable speed motor 12. Thefirst overhead track 11 is linear and runs substantially in thelongitudinal direction of the conveyor means 1. In a variant embodiment,which is not shown in the figures, this overhead track 11 may besubstantially parallel to the conveyor means 1, also above thefall-plate 2, in such a manner that the start board 7 and the firstcarriage 10 undergo substantially the same up- and downward movementwhen the start board is moving over the conveyor means 1. In order tocompensate in this case for possible distance differences between theconveyor means 1 and the first overhead track 11, measured in thedirection of the first link arm 9, this link arm 9 can be hingedlyconnected to both the carriage 10 at hinge 13 and to the start board 7.

When the foam machine is enclosed in an enclosure, for example forcontrolling the pressure during the foam process as disclosed in thePCT- Patent Application n° PCT/EP91/02176 of the same applicant, thefirst overhead track 11 is preferably linear so that the height of thefoam machine is the same over its whole length. In this case, the firstlink arm can also be hingedly connected to the first carriage 10 and tothe start board 7. However, in order to prevent that the speed of thestart board 7 when moving over the fall-plate 2 would be too high inrespect to the speed of the bottom sheet 4 moving also over thisfall-plate 2, due to the counterclockwise rotation of the first link arm9 around its upper hinge axis 13, the angle α between the first link arm9 and the first track 11 is maintained constant during the downwardmovement over the fall-plate 2. This is realised in the embodiment shownin FIG. 1 by the fact that the first link arm 9 is slidably connected toboth the first carriage 10 and to the start board 7.

The slidable connections between the link arm 9 and the carriage 10 maybe directed in a manner such as to permit a substantially up- anddownward movement of the start board 7. Preferably, the slidableconnections are, however, directed somewhat obliquely so as to reducethe speed of the start board 7 over the fall-plate 2 still somewhatfurther in order to adjust the speed of the start board still better tothe speed of the moving bottom sheet 4 by compensating for the downwardspeed component of the start board 7. By minimizing the speeddifferences between the start board 7 and the bottom sheet 4, the risksof damaging this bottom sheet are considerably reduced.

In order to further limit the risks of damaging the bottom sheet 4,means are preferably provided for reducing the pressure of the startboard 7 onto the bottom sheet 4. This can be realised for example byusing a counter weight to pull up the link arm 9 in the slidableconnection with the carriage 10 or by providing a constant hydraulicpressure in this connection exerting an upwards force onto the link arm9. The link arm 9 can then be fixedly connected to the start board 7 oranalogous means can be provided in the slidable connection between startboard 7 and link arm 9 to exert an upward force upon the start board 7.

In the embodiment shown in FIG. 1, the link arm 9 is hingedly connectedto a slidable member 14 in the carriage. The downward rotation of thelink arm 9 is, however, limited to the angle α in position I and II ofthe link arm in FIG. 1.

In position II, the foam has completed its rise and is sufficientlystable. The motor 12 is then accelerated so that a gap is createdbetween the front of the foam block and the start board 7. The means forremoving the start board 7 from the conveyor means 1 comprise aprojection 15 which lifts mechanically the link arm 9 and the startboard 7 as they pass this projection 15. FIG. 2, which is a top planview of the device of FIG. 1, shows that the projection 15 is fixed tothe overhead track 11 and that the link arm 9 comprises two parallelarms which are lifted both by this projection 15. It is clear thatinstead of mechanical lifting means, use can for example also be made ofhydraulic lifting means.

FIG. 3 shows, on a larger scale, the start board 7 of the devicerepresented in FIG. 1, being connected, however, by means of a verticallink arm 9 to the carriage 10. In fact, the link arm 9 may be disposedunder different angles depending mainly onto the available space for thedifferent components such as the overhead track 11 and the carriage 10.The start board 7 comprises a roller 16 for rolling over the conveyormeans 1 so that the risk for damaging the bottom sheet 4 is furtherreduced. In order to keep the foaming reaction mixture away from thisroller 16, a lower flap 17 is hingedly connected to a base part 18 ofthe start board 7.

The start board 7 shown in FIG. 3 comprises moreover an upper flap 19which is also hingedly connected to said base part 18 and which ismaintained in its erected position by means of springs 20. In this way,the upper flap 19 can be pushed down, as shown in FIG. 4, when ittouches any vertical obstruction, for example when the foaming machineis enclosed in a narrow enclosure.

FIGS. 5 and 6 show the stop board 8 and the mechanism for moving thisstop board 8 along the conveyor means 1 at the end of a production run.As it can be seen from FIG. 6, the stop board 8 is composed of twomutually movable panels 21, 22, which partially overlap one another topermit width change. The panels 21, 22 are each hingedly connected to aseparate carriage 23 and 24 respectively by means of cranked arms 25 and26 respectively. Each of the carriages 23 and 24 is movable over aseparate overhead track 27 and 28 respectively by means of a secondvariable speed motor 29. The overhead tracks 27 and 28 are eachconnected to the sidewalls 30 and 31 of the fall-plate 2 by means ofbrackets 32 and 33 so that as the foam width is varied, the stop board 8is automatically set to the correct width.

The means for positioning the stop board 8 onto the conveyor means 1comprise a stop 34 which maintains the stop board 8 in the rest positionI shown in FIG. 5. By moving the stop board 8 into position II, it isautomatically lowered onto the fall-plate 2. During its movement toposition III, it pushes the foaming reaction mixture 35 forwards whilethis is moving over the fall-plate 2 so as to obtain the desired endblock profile.

Even as the stop board 8, the start board 7 can also be composed of twomutually movable panels in order to allow an automatical widthadjustment of the start board. Without such an automatical adjustment,the width of the start board has to be adapted to the width of the foamto be produced by replacing the start board.

An automatical width adjustment is also possible by using a start boardand/or a stop board which comprises a central part, two side flaps whichare hingedly connected to this central part and means for urging theside flaps towards the side walls 30, 31. These urging means can beformed for example by the fact that use is made of resilient side flaps.Further they can comprise springs or other resilient means. The centralpart itself can be composed of different elements, for example of thetwo mutual movable panels 21, 22.

Although in the above description, there is referred to a start board 7and a stop board 8, the function of these board can possibly also befulfilled by one and the same board 7, 8. Such an embodiment is shownschematically in FIGS. 7 and 8. In this embodiment, the board 7, 8 isfixed to the arm 9 which is hingedly connected to carriage 10. At thebeginning of a production run, the board 7, 8 is lowered from a restposition I into position II onto the conveyor means 1 as shown in FIG.7.

FIG. 8 shows the board 7, 8 in a third position III, wherein it islifted above the end of the first bottom conveyor 3. From this position,the board 7, 8 is moved along the overhead track 11 by means of themotor 12 back to the beginning of the conveyor means 1, near the trough6, and is lowered there again at the end of the production run, fromposition I to position II. The board 7, 8 is then moved along theconveyor means 1 to push the reaction mixture forwards to therebyincrease the height of the end portion of the produced slabstock foam.In this embodiment, the means for lowering and lifting the board 7, 8are for example hydraulic means which have not been represented in FIGS.7 and 8.

Before starting a production run, the bottom sheet 4 is unrolled fromfeed mandrel 36, applied over the fall-plate 2 and the first bottomconveyor 3 and fixed to the rewind mandrel 37. The side sheets 38 areunrolled from feed mandrels 39, and fixed by means of double adhesivetapes to the side conveyors 40 and 41 and to side rewind mandrels 42.The lateral sides of the bottom sheet 4 are folded somewhat upwardsagainst the side sheets 38.

At the beginning of a production run, rewind mandrel 37 exerts a largeforce onto the bottom sheet 4 to pull the front portion of the foamblock over the fall-plate 2. Due to the considerable length of thebottom sheet 4, for example about 30 m, this bottom sheet may contractlaterally so that it does not cover the total surface of the conveyormeans. In order to prevent this, the invention proposes means foranchoring the bottom sheet 4 near the fall-plate 2 onto the first bottomconveyor 3 at the beginning of a production run.

In a first embodiment, these anchoring means comprise a flat weighthaving such a surface that it does not fall within the gap between theend of the first bottom conveyor 3 and the rewind mandrel 37.Additionally, means can be provided for lifting the weight as it reachessaid gap.

In an effective embodiment of the invention, said anchoring meanscomprise a transverse row of pins 43 mounted onto the first bottomconveyor 3 and for automatically retracting these pins during the firstrevolution of this bottom conveyor 3. These retracting means ensure thatthe bottom sheet 4 is liberated from the pins at the end of the bottomconveyor 3.

Such a mechanism is shown in FIGS. 9 and 10. The bottom conveyor 3 ismade up of a series of transverse bottom slats which are hingedlyconnected to each other in such a manner that they can curve around thedrive sprockets 44 of the conveyor 3. FIGS. 9 and 10 show two adjacentbottom slats 45 and 46 respectively in a flat position and in a positionwherein these two slats are curved around a sprocket 44.

The row of pins 43 is rotably mounted on a transverse shaft 47 fixed toslat 46 in such a manner that the pins 43 can rotate from a retractedposition wherein they are swung down under the surface of the conveyorto a position wherein they are turned over backwards as shown in FIG.10. Springs are provided but not represented in the figures, to urge thepins 43 into the retracted position. These springs may act directly uponeach the pins 43 or upon the shaft 47 in the event the shaft 47 isrotably fixed to slat 46.

In order to prevent the pins 43 from turning backwards when pulling ontothe bottom sheet 4, at least one lever 48 is mounted on the shaft 43,and more particularly on the pins 43, the rotation of which lever 48 islimited in the flat position by means of a stop 49 on the adjacent slat45, as shown in FIG. 9. When the pins reach the end of the conveyor 3,they should release the bottom sheet 4. As shown in FIG. 10, the releaseof the bottom sheet 4 is assured by a backward rotation of the pins 43.The backward rotation is possible due to the increased distance betweenboth slats 45 and 46 when they are curved around the sprocket 44 so thatlever 48 can freely pass stop 49 on slat 45. When the bottom sheet 4 isreleased, the springs swing the pins 43 back into the retractedposition. In this position they are lying in cut-outs 50, underneath thesurface of the conveyor. During the further rotations of the conveyor 3,they remain into this position until they are manually lifted to anchora new bottom sheet 4 at the beginning of a next production run.

It will be clear that the invention is not limited to the hereinabovedescribed embodiments but that these embodiments can be modified in manyways within the scope of the present patent application.

First of all, the start board and its control means could be designed insuch a manner that they can be used to control the start profile as wellas the end profile of the produced slabstock foam.

Further, use can be made of one and the same overhead track for both thestart board and the stop board. To control the width of start boardand/or stop board, they can be composed of two partially overlappingpanels which can be displaced for example hydraulically along each otheror as described hereinabove with respect to the stop board, byconnecting these panels to two different displaceble overhead tracks.

The width of start and/or stop board can optionally also be controlledby means of hinged side flaps which are pushed against the side walls orthe side conveyors for example by means of springs. Such side flaps canalso be provided in combination with other width adjusting means, inwhich case they provide for a precise width adjustment so that a lessaccurate control of the other width adjusting means is required.

Even as the stop board, the start board can also be composed of twopanels which are connected to two separate overhead tracks, optionallyto the same overhead tracks as the stop board.

We claim:
 1. A device for the continuous manufacture of slabstockpolyurethane foam comprising:conveyor means and means for driving saidconveyor means; a mixing head for mixing polyurethane reactioncomponents containing a blowing agent; means for discharging thereaction mixture from said mixing head onto said conveyor means at thebeginning of a production run wherein said discharged reaction mixtureexpands to form a slabstock of foam on said conveyor means; a startboard and a stop board; means for positioning said start boardtransversely onto said conveyor means adjacent the place of discharge ofthe reaction mixture at the beginning of a production run; means formoving said start board along said conveyor means in a first phase and asecond phase, wherein in said first phase said start board obstructs thereaction mixture moving over said conveyor means, to thereby increasethe height of a front portion of the discharged reaction mixture so thatthe height of a front portion of the foam produced will have a heightsubstantially equal to a height of a subsequent portion after thereaction mixture has achieved full rise expansion, and wherein in saidsecond phase said start board is moved at substantially the same speedas said conveyor means; means for removing said start board from saidconveyor means; means for positioning said stop board transversely ontosaid conveyor means adjacent the place of discharge of said reactionmixture when discharge of the reaction mixture has stopped; and meansfor moving said stop board along said conveyor means so as to push thereaction mixture ahead relative to said conveyor means and therebyincrease the height of an end portion of the discharged reaction mixtureso that the height of an end portion of the foam produced will have aheight substantially equal to a height of a previous portion after thereaction mixture has achieved full rise expansion.
 2. The device asclaimed in claim 1, wherein said start board moving means maintains thestart board stationary, in said first phase, and moves the start boardat substantially the same speed as said conveyor means in a secondphase, when the reaction mixture reaches a predetermined height againstthe start board.
 3. The device as claimed in claim 2 comprising meansfor actuating said conveyor drive means substantially simultaneous withmovement of said start board along said conveyor means.
 4. The device asclaimed in claim 1, wherein said start board removing means comprisesmeans for accelerating movement of the start board in the direction ofmovement of the discharged reaction mixture on said conveyor means andmeans for lifting the start board after a predetermined gap is createdbetween the front portion of the foam formed from the dischargedreaction mixture and the start board.
 5. The device as claimed in claim1, wherein said stop board positioning means is adapted to position saidstop board within a distance of 3 m from the place of discharge of thereaction mixture.
 6. The device as claimed in claim 5, wherein said stopboard positioning means are adapted to position said stop board within adistance of 0.5 m from the place of discharge of the reaction mixture.7. The device as claimed in claim 1, wherein said start boardpositioning means is adapted to position said start board within adistance of 3 m from the place of discharge of said reaction mixture. 8.The device as claimed in claim 7, wherein said stop board positioningmeans are adapted to position said stop board within a distance of 0.5 mfrom the place of discharge of the reaction mixture.
 9. The device asclaimed in claim 1, wherein said start board positioning means and saidstart board moving means comprise a first overhead track runningsubstantially in the longitudinal direction of the conveyor means, afirst carriage movable along said first track, a first variable speedmotor for moving said first carriage along said first track, at leastone first link connected at a first end to said first carriage and at asecond end to said start board, and means for lowering the start boardby means of said first link arm onto the conveyor means.
 10. The deviceas claimed in claim 9, wherein said first link arm is slidably connectedto at least one of said first carriage and said start board wherebycompensation for differences in distance between said first overheadtrack and said conveyor means can be accomplished.
 11. The device asclaimed in claim 10, wherein said conveyor means comprises a fall-plateand a conveyor, and where by said slidable connection allows verticalmovement of the start board when the start board is moving over thefall-plate.
 12. The device as claimed in claim 1, further comprisingmeans for reducing pressure exerted by the start board onto the conveyormeans.
 13. The device as claimed in claim 1 wherein said start boardcomprises at least one roller for rolling over said conveyor means and alower flap hinged about a substantially horizontal axis of the startboard and provided to contact the conveyor means obliquely between saidroller and the discharged reaction mixture.
 14. The device as claimed inclaim 1, wherein said start board comprises an upper flap which ishingedly connected to a base part of the start board and which foldsdown when colliding with an obstacle and further comprising resilientmeans for urging said upper flap to its erected position.
 15. The deviceas claimed in claim 1 wherein at least one of said stop board and saidstart board are provided with means for automatically adjusting theirwidth to the width of the discharged reaction mixture.
 16. The device asclaimed in claim 15 wherein at least one of said stop board and saidstart board comprises at least two mutually movable panels and means formutually moving these panels to adjust the width of the respective boardto the width of the discharged reaction mixture.
 17. The device asclaimed in claim 16 wherein said movable panels have portion overlappingone another and are each fixed by means of a separate link arm to acarriage movable over an overhead track in the longitudinal direction ofthe conveyor means, said device further comprising width adjusting meansfor adjusting the distance between said two link arms, said devicecomprising in particular one carriage and one overhead track for each ofsaid two panels, each of said overhead tracks being fixed to one of twotransversely adjustable side walls along a first part of said conveyormeans.
 18. The device as claimed in claim 15 wherein at least one ofsaid stop board and said start board comprise a central part, two sideflaps which are hingedly connected to said central part and means forurging said side flaps outwardly so as to adjust the width of therespective board automatically to the width of the discharged reactionmixture.
 19. The device as claimed in claim 1 wherein said start boardand said stop board are one and the same board.
 20. The device asclaimed in claim 1, wherein said conveyor means comprises:a fall-platefollowed by a conveyor, a bottom sheet disposed longitudinally over saidfall-plate and said conveyor, and means for anchoring said bottom sheetto the conveyor at a location adjacent said fall-plate.
 21. The deviceas claimed in claim 20, wherein said anchoring means comprises atransverse row of pins mounted onto said conveyor and means forautomatically retracting said pins.
 22. The device as claimed in claim21, whereinsaid conveyor is comprised of a series of transverse slatsmounted for rotation about a sprocket, and hingedly connected to eachother, said hinge connection having an axis; said row of pins rotatablymounted on a transverse shaft fixed to one of two adjacent slats at aposition outward from the hinge axis of the two adjacent slats, said twoadjacent slats defining cutout portions; and said retracting meansfurther comprisingspring means for urging said pins from a positionwherein they project through the cutout portions between said two slatsto a retracted position, at least one lever mounted on said shaft at afixed angle with respect to said pins, and a stop provided for saidlever on the slat of said two adjacent slats which does not have saidtransverse shaft fixed thereto, said stop limiting the rotation of saidlever, thereby preventing a backward rotation of the projecting pinswhen said two adjacent slats are substantially in the same plane, andsaid stop allowing a backward rotation of the projecting pins when saidtwo slats are in rotation about a sprocket of the conveyor so that adistance larger than the length of said lever is obtained between saidshaft and said stop.